Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $236.95   9.523%   $259.5147   $259.51   $259.50   $259.50  
  Purchase #2 $12.73   11.551%   $14.2004   $14.20   $14.20   $14.20  
  Purchase #3 $57.76   4.128%   $60.1443   $60.14   $60.15   $60.10  
  Purchase #4 $138.80   12.863%   $156.6538   $156.65   $156.65   $156.70  
  Purchase #5 $187.78   8.749%   $204.2089   $204.21   $204.20   $204.20  
  Purchase #6 $154.66   11.847%   $172.9826   $172.98   $173.00   $173.00  
  Purchase #7 $71.57   6.587%   $76.2843   $76.28   $76.30   $76.30  
  7 purchase totals = $860.25       $943.9890   $943.97   $944.00   $944.00